Modulated wave modifying apparatus



Dec. 7, 1948. R. H. VARIAN 2,455,393

MODULATED WAVE MODIFYING AIQPARATUS Filed June 9, 1943 s Sheets-Sheet 1 uficher voliuge (v INVENTOR RUSSELL H. VARIAN BY L ATTORNEY L.P. FILTER D.C. AMPLIFIER Patented Dec. 7, 1948 UNIT ETD STATES MODULATED WAVE -MQDIFYING AlhARAT-US" ware 21 Claims.

The present inventionis relatedtothe art including velocity variation electron discharge tube devices'and especially to such devices of the type shown in Varian Patent No. 2,242,275; issued May 20, 1941. The present invention is more particularly directed to apparatus and'methods for utilizing such devices for the control of modulation upon an ultra high frequency carrier wave, such as in the centimeter wavelength region.

It has beendiscovered thatvelocity variation devices of the above type may be effectively utilized as amplitude limitersor percentagemodulation control devices in addition -to their ordinary uses as amplifiers andyoscillators. Accordingly,

it isan object of thepresent-inventionto provide I improved apparatus and" methods for limiting the amplitudeof an ultra high frequency carrier wave; whereby random or othervariations in amplitude such as duetto noise or other causes may be substantially eliminated.

It is another object of the present invention to provide improved apparatus and-methods for changing or controlling the percentage, modulation of a modulated ultra high frequency carrier wave.

It is still another object of the invention to provide'improved apparatus for modifying the modulation of a modulated wave'and toautomatically maintain the modified condition of the wave'at a desired value.

It 'is a, further object of the present invention to provide improved ultra high frequency mixer means useful in the above-described invention, and also generally useful.

It is a still further object of the'present invention to provide improved apparatus andmethods for eliminating the carrier component of an ultra high frequency modulated wave to form a carrier suppressed wave.

It is still another object of the present invention to provide improved apparatus. and methods for increasing the percentage modulation of an ultra high frequency modulated wave.

It is yet another object of the present invention to provide improved apparatus and methods for,

reversing/the, phase of the modulation upon a modulated ultra high frequency wave,

It is a further object of the invention to provide improved frequency-independent apparatus for carrier suppression or percentage modulation control of highfrequency modulated waves.

Other objects and advantages-of the present invention will become 2 apparent from consideration of the following-specification and drawings, wherein:

travel through drift tube- Fig. ;1 shows aschemat'ic diagram of the velocity variation electron discharge; tube of thejlpresent invention.. i

Fig. 2 shows. a graph useful in explainin'g the theory of. operation. accordingj -to' the presentj in? vention.

Fig. 3 shows various. voltage versus timejjcurves useful in explaining the various typesoffpperation according .to the present invention;

Fig. 4 shows an automatic circuitjfor producing the improved results according to the presentin vention.

Fig. 5 shows a detailed view ofthe balanced mixer-ofFig. 4.

Fig. 6 is a block diagram of an electronicjclrr cult adapted to producethe same resultsa's-the device of.Figs..1 or 4.

Fig. 7 is a graph useful-in explaininglthe operation'of the devicev of Fig. -6.

Figs. .8-12 are schematic block diagrams of modifications of Fig, 6;

Referring to-the drawings; Fig. 1 schematically showsla velocity variation electron discharge device l l,- commercially known. asthe Klystroml which is described in the above-mentioned Varian Patent No. 2,242,275. Asis well known, suchdevices include a pair roffcavity resonatorsj l2 and I3 havingv respective pairs of electrorrpermeable grids l5, IS-and I1, l8-separated. by a field-free drift-space defining tube. M. ;An electronlstream is projected from' a cathode. l9.bymeans of-Ian accelerating battery 2| and .successi'vely passes through the gaps between grids l5, .IB'and-LHI. .(8. The input or buncherresonator l ZmaybeeX'cited wi-thultra high frequency energy. by means .ofan; input connection, such. as an input concentric line 22', and .corresp'ondinghigh frequency energy-j-may be. abstracted from..the-output.or. catcher resonator 13 by wayof. a similar couplinglihlaorterminal 23; The high frequency electromagnetic fieldexistingbetween grids l5 and 1-6. servesto periodically vary, the velocityof. the electrons passing thereth-rough-.- These velocity-varied electronsbecome grouped or bunched; during; their l4 and .deliver corresponding amplified ultra high frequenoy energy to the resonator, l3 upon;passing throughf grids l1 and- 3. As-isdiscussed in the-; alooye-,-mentionedPatent No; 2,2e2,-275 the presentapparatus .may serve as an-ultra high frequency amplifierjor an ultra high; frequency regenerative oscillator or a regenerative amplifier; The; operatig oi resonators 1.2 and l 3 -upoz1 theelectron beam; is the sameaas though-yam alternating voltagewere impressed betWeeI-r their rcorresi qnding grids-J 5,

tion signal taken for 3 IE or l1, [8. This effective voltage between grids l5, [B will be hereinafter termed the buncher voltage, and the corresponding effective voltage between grids I1 and i8 will be termed the catcher voltage.

It has been found that, as the amplitude of the ultra high frequency buncher voltage is varied, as by changing the energy supplied to line 22 or by changing the coupling between line 22 and buncher resonator l2, the catcher voltage produced will vary in accordance with the curve shown in Fig. 2, which has the form of the well-known Bessel function of first order having its argument proportional to the buncher voltage. This curve shows that the catcher or output voltage is an oscillating function of the input or buncher voltage. In operating the device as an amplifier or regenerative oscillator, in the manner described in my above-mentioned Patent No. 2,242,275, the buncher voltage is adjusted to a value such as Vi, so that the tube operates approximately at the point i of the characteristic of Fig. 2. At this point it will be seen that an increase in buncher voltage will produce a substantially proportional increase in catcher voltage, and accordingly the device may act conveniently as a linear amplifier for a modulated wave input.

According to the present invention, the device of Fig; 1 is'caused to operate'as an amplitude limiter or modulation suppressor, as a modulated wave inverter, as a carrier suppressor, as a percentage modulation increasing circuit, or as a percentage modulating decreasing circuit, depending on the operating point chosen.

For example, if the buncher voltage is adjusted to the value V2 corresponding to point 2 of the characteristic, at which the characteristic has a maximum value, it will be seen that Variations in the amplitude of buncher voltage over a considerable range will have negligible effect upon the catcher voltage. Therefore, if a modulated input wave of relatively small percentage modulation and producing an average buncher voltage V2 is fed to the buncher resonator 12, the variations in amplitude of this wave caused by its modulated character will be virtually eliminated by the device, and a substantially pure unmodulated wave will be produced in the output line 23. In this way the device will act as a voltage regulator (maintaining constant output amplitude), as a modulation suppressor, or as an amplitude limiter.

In this instance, the output amplitude remains substantially constant despite variations of the input amplitude. This condition is illustrated in Fig. 3, in which curve A illustrates a modulaillustrative purposes only as being approximately a sine wave. Curve B illustrates a carrier wave amplitude modulated in accordance with the signal of curve A. If such a wave is fed to the buncher resonator 12 when the device is operating with the average buncher voltage at point 2 of the oscillating characteristic of Fig. 2, the result will be an output wave derived from output line 23 of substantially the form shown in curve C, in which the variations in amplitude of the wave are substantially suppressed. Accordingly, as suggested above, the device with this condition of operation will operate to yield a substantially constant output amplitude despite the variations of input amplitude. It will thus operate to eliminate any modulation, whether intentional or involuntarily caused, such as by noise impulses.

If the device of Fig. 1 operates at point 3 of Fig. 2, as by supplying an average buncher voltage V3, it will be seen that an increase in the buncher voltage from the value Vs will produce a decrease in the catcher voltage, and correspondingly, a decrease in the buncher voltage produces an increase in the catcher voltage. If the wave of Fig. 3B is again supplied to the device of Fig. 1 with an average amplitude V3, the output derived from the catcher resonator 13 will be as shown in Fig. 3D; namely, the modulation envelope has been reversed in phase, and the device therefore operates as a modulation phase inverter. It is to be noted that it is only the modulation envelope which is reversed in phase. The actual ultra high frequency alternations are not affected.

The present circuit may also be utilized to increase the percentage modulation of the wave supplied to its input. Thus, if the input wave shown in Fig. 3B is so adjusted that the maximum amplitude vmax. of its envelope is equal to V4, which is the value of the buncher voltage pro ducing operation at point 4 of the characteristic of Fig. 2, it will be seen that, at this value of the buncher voltage, zero voltage will be received at the catcher. For voltages differing from this maximum, the output of the catcher will increase in substantially linear relation to the decrease in the buncher voltage. Accordingly the output wave will be of the form shown in Fig. 3E; namely, it will have its percentage modulation increased to substantially per cent, with a phase inversion of the modulation envelope. It will be clear that for average amplitudes of the buncher voltage between the value producing curve E and that producing curve D, the percentage modulation of the input wave may be changed from its original value to any value to 100 per cent by a suitable choice of operating point. i

A further type of operation may be obtained by operatin at point 4, at which point the buncher voltage V4 yields zero catcher voltage. In view of the substantially linear character of the characteristic on either side of point 4, the apparatus may then operate to entirely suppress the carrier component of the modulated wave supplied to the buncher resonator 13. Thus, if the wave of Fig. 3B, having an average amplitude V4, is supplied to the input of the device of Fig. 1, the resultant output voltage derived from catcher resonator l3 will have the wave shape shown at Fig. 3F, which will be recognized as a carrier-suppressed wave. In this Way a simple modulated wave, such as in Fig. 33, may be converted to a carrier-suppressed Wave, as in Fig. 3F.

As another illustration of the use of the present device, it may be operated at point 5 of Fig. 2, that is, with the average amplitude Vave. of the wave of Fig. 313 having the value V5, which is so selected that the minimum amplitude Vmin. of the wave of Fig. 33 produces a buncher voltage V4. When this is done, the result obtained from the catcher resonator l3 will be the wave of Fig. 3G, in which it will be seen that the percentage modulation has been increased to 100 per cent without the phase inversion produced in Fig. 3E.

Operation at point 6 of the characteristic of Fig. 2 will produce the same constant voltage output as is derived under the condition illustrated in Fig. 3C when the average input amplitude Vave. is adjusted to have the value Vs.

However, q in*- this case the ultra" high frequency wave will* be phase inverted with respect tothat obtained by operating at' point '2. I

If -the maximum amplitude-*Vmax. of the input wave of Fig; 3B is adjustedto have the value V1: corresponding to the second zereot the curveof Fig. 2, in which case-the average' input amplitude 'Vave. will produc'e abuncher voltage vv, the Wave of Fig: 3E will again be -produced; having themodulation reversed in phase: Thephase" of thehigh-frequenCyoscillations isalso reversed with respectto operationwvith maximum-input at 4: By operating with the I voltage input amplitudevtva at point '8,-' -'at--an+ average buncher voltage Va-I a further carrier suppressed wave similar to*Fig.-'3F 'will-be produced in-theoutput. Again -by= operating with the minimum ampl-itude Vmm; "of the input wave*-to-produce abuncher voltage Vs; in whic'l rcase' the opera-ting point will beat abunchei voltage Vs}- the output wave of Fig. 13Gwi'll' be obtained'i" Again whenoperating at-point I'll, the-characteristicof- Fig; 3C-=will be produced:

In this same manner further opera-tingpoints may be'chosen along-- the' -characteristic' of Fig. 2; which will produce any -ofthe types ofopera=- tion-- discussed-above and also -many other types intermediate those-*described.-- Also, the-amount of" decrease of percentagemodulation may be variedby' selecting various pointsalong thecharacteristic, since the decrease-in percentagemodulation will dependupon the slope of the characteristic; divided *by the heightof-the curve above zero."

It will be noted that the slopesexistingatwarious points inthe curvecontinuously become-less and less as the higher modes --of operation-- are reache'de" Therefore fonbest" operation as an amplifier in the'mannen discussed in my--Patent No: 2,242,275,- the operating-point should remain at point -I which has the steepest'slope anywhere along the curve; and therefore produces'the'highest gain.-

In order'to be able to maintainoperation--at. any predetermined point of thecharacteristic of Fig: 2, to derive any of the -typesof opration already discussed; use may beha'd oi the system of-Fi'g. 4; which shows a system-fol" controlling the input to'resonator l2 of-the-device 'H. For,

this purpose-an ultrazhighgffrequency amplifier 26; also preferably of the velocity modulation type, is supplied-with the input wave corresponding to-the wave 'ofFig. 3B bymcans-ofits'input concentric line2'l coupled to its buncher resonator -28'; The output derived'iromthe' catcher resonator'29 is thenyfed by line-22"tovresonat'or I2, and also is fed to a ba'l-anced'gultra high1frequency mixer 3! by line 22'. Baianced mixer 3lis also supplied with energy' derived irom catcher resonator l'3'of the-controlleddevice-H, as 'by wayofthe couplingline" 32 'tsh'ownfmore in detailin'Fig. 5; and-is thereby adapted t'cproduce anoutputjhaving a waveform corresponding to the product-of-the instantaneous Wave forms of its inputs, in accordance withtheweli-known theory of-balancedmixers;

Fig. 5 shows inmore detailthe, arrangement of the balanced mixer 31. The-'couplingline llz comprises a Urshaped-conductor 39"lbcated'within the electromagnetic field-'ofthecatch'er l3 and having a central*conductor"connected to the centerofthe-U -shaped portionto-iorm two coupling' -loopsi xifl; 4-1. This centraluconductor45*is connected to, 0r forms an extension-of} the centraltconductonof line ZZ connected- 'to 1-ine 22"- 6 supplyingenergyfrom amplifier 26 m thefbuncher l 2! The-outer conductor: of line' 221i isconnected to the outer conductor fl of the transmission' line 32"? In this way-the current. fiowingviinv therinner conductor of the trarrsmissi'ontline 22- is connected in'series with each! f th'e currentsIinducedLin thetw o loops 40, Ma these -two-loops total will be ofloppositeixphase, and preferablyi the currentsproduced inith'e inner conductor :41 is adju'sted in i phase; by meanssoi any suitable .pha'seash-ifting mechanism: inserted in line 22 -(not shown hso-as torb'e' in phaseopposition t-o one otsthe -tWlO 1100p i currents and in phase-concurrence with t'he iother. These-resultant cun'entsaintthdlegsswfii39!" of conductor:39 are then rectifiedebysrespective=rectifiers 43Fa=nd44 connected 'in series :therewithu: t

It wil'l be:olearthatiwhenzzero:.current is :picked 43 a-ndi4 4: being int-opposition with: respect 'to the currentspfl'owingu inuconductor. 4 I will. produce zero: direct ;currentcoutput in-itheroutput' loads 46, which-i maysb'e connected-to a load resistor 59. When a; currentofzpredeterminedlphase is induced inthe two loops; 499417bneiof'thhua rents supplied: to rectifiersr 43 and: 4-4 -will be increased and the other will be decreased, producing; a direct cu-rrenttoutputaof:predeterminedpolarity; When reverse; phase-currents? are-"induced in; they loops .402. 4|, theformerlyxjdecreased currentv is now increased andathe formerlywincreasecr;current .is now decreased: -producingi ian=o opposite: polarity .directcurrent Loutputz;

It will be'seemthat zif;the input to .buncheri2 is an unmodulatedepure:carriensand ifthe deviceszl-l is operatingtatzpoint dict-the:characteristic of EigtZ, the'catcherwoltagegwiilhavezero amplitude; and; accordingly; :the mixer -3 i: will: have zerov outputaastdiscussedw above. I

Fora buncher voltage-either less than; or greater :thamthe: walue. V4 requiredtooperate at point 4; a-;ca-tcher= voltage-:willtappear in .the catcher 1:3; whose amplitude will be: substantially proportional-*to-the deviation of the actual 1 buncher .voltagevfromi the value V4 for reasonable BXOUI'SiOIIScflOIIi V4: Howeveiyas theebunc-her voltagen'increases :from aavalue less thanv V4 to :a valuegreaterthan V4,! ,the: phase oft: the! ultra high: frequency? oscillations-g produced: 'in: the catcher resonator l3 will reverse; lilteiSpthE phase-sense ofthis-catcher voltage-dependsionthe sense of excursion of r theivbunc-hen voltage from the value V42 Therefore;- if the-input ttol theimixer 3l derived from line-221GB adiiusted-inzphase with-.-respect to the-input derived-from-line '32; to beeitherin relative phaseconcu-rrence-:or1phase opposition, it will? be seen that 'thedirectcurrentoutput from mixer 3| will reverse-polarity as =the buncher voltage passes-throughthevvalue-V4; and that the ma'gnitude m? this direct current output will depend upon :thedeviation of the-actual'buncher voltages fromwthe valueww} This; feature is uti-lizedz-- the present circuit to" automatically control: the actual 'buncherrvoltage fed: to; buncher- I-2 to,- maintain the=:catcher l3 output atva desiredmointof the-characteristic 'of-Fig;.-- 2:

Thus;:-:-the: output:45eoL-mixerc3i is passed through low passfilterr33;whichpermits only the direct .current component- 0fthetmixer-outputl-to pass therethrough. ,7 .This-i direct current. output is then amplified; if desired; in. assuitable direct current" amplifier 34; and, i'simpresseduponx the controlfgrid 36*oftheamplifier'lfil' l 1 iswvell known the""amplification of a The? currents. induced: in

Klystron amplifier, such as 25, depends-upon the beam current passing therethrough. By thus controlling the beam current from theoutput of mixer 3|, the output of catcher 29 can be adjusted to give a desired voltage for buncher l2. For example, let it be supposed that it is desired to operate at. the point V4 of the-charac-- teristic of Fig. 2. At this point, as hasbeen discussed, the mixer output should be zero. vIf the buncher voltage departs from the value Vathis will be sensed by the appearance of a direct current output from mixer 31, the polarity ofthis output depending upon the sense of the deviation of the buncher voltage from the value V4, and the output magnitude depending upon the amount of buncher voltage deviation.

Let it be assumed that a negative voltage is obtained from direct current amplifier 34 when the buncher voltage is higher thanzthe value V4, as can be obtained by properly poling amplifier 34 to grid 35. This negative voltageapplied to grid 36 decreases the output of Klystron amplifier 26 and thereby decreases the voltage of buncher f2. By making the amplification of direct current amplifier 34 relatively large, the system can be made to operate substantially exactly at the voltage V4- correspondingly, if the actual buncher voltage is too low, a positive output voltage will be derived from' direct current amplifier 34 which, when applied to grid 36, will increase the output of Klystron amplifier 26 and will therefore increase the voltage of buncher I2. The buncher voltage can thereby be maintained at the desired operating point illustrated asV4;

If it is desired to operate the device at any other operating point, it will be seen that for this operating point a particular mixer output, or output from direct current amplifier 34, will be derived. This output may be effectively cancelled out by a bias derived in any suitable manner-, as from an adjustable direct current source, such as battery 38, in series with grid 36; so' that grid 35 is properly biased to produce a buncher voltage which in'turn from direct current amplifier 34 just sufficient to maintain this desired-buncher voltage; By proper choice of the bias of battery 38, any desired operating point may be automatically maintained.

t will be noted that in each of the typesof operation discussed above, and especially in the type of operation wherein the carrier component of the modulated wave is removed, the apparatus is responsive, not to frequency, but solely to the amplitude of the modulated wave. In this respect the present apparatus constitutes a distinct change from prior parctice in which a carrier is usually removed by filter means or other frequency sensitive apparatus.

The same principle may be applied to eliminate the carrier component of a modulated lower frequency wave. A block diagram for such a system is shown in Fig. 6. Thus, the modulated wave is fed to a pair of amplifiers I and II whose input versus output characteristics may be asshown by the correspondingcurves of Fig. 7. The outputs on this characteristic may be that at a particular harmonic of the input, or at the same will produce an output frequency as the input. It will be seen that these put voltages differing from V1, the outputs of the two amplifiers will be unequal, and, in fact, the difference between these outputs may be as rep resented by the resultant curve II I shown in Fig. 7, which is another form of oscillating function, somewhat similar to that of Fig. 2. The difference between the outputs maythen be obtained by a suitable combining circuit 5|. 1

If the average amplitude of the modulated input wave is chosen oradjusted to have the value V1, then the output from combining circuit 5! will have the carrier component suppressed in the same manner discussed with respect to Figs. 1 to 5. This is produced by the characteristic 1-41 of Fig. 7, which gives zero output at the average amplitude of the modulated wave and has substantially linearly varying output -at;tl 1e selected harmonic of the carrier with respectto deviations of the amplitude of the input modulated wave from this average value. Furthermore, the phase reversal in the output of the combining circuit assures that the output wave will be a true carrier-suppressed wave. The circuit of Fig. 6 therefore constitutes essentially anamplitude discriminator.

The amplifiers I. and II may be provided in several different manners, of which two are illustrated in Figs. 8 and 9. In Fig. 8 the amplifiers I and II are chosen to have differing amplification characteristics. Then the input modulated wave is supplied in opposite sense to the control grids of the amplifiers I and IIby Way of a coupling transformer 52. Preferably, although not necessarily, the amplitude of the voltage applied to one of these control grids is greater than that applied tothe other. v

The outputs from the amplifiers I and IIare additively combined in the primary 53 of anout- ,put transformer 54. One of the amplifiers, shown as amplifier II, is coupled to only a portionof primary 53, the other being coupled to the entire primary 53. By suitable adjustment of the relative couplings of the two amplifiers to theprimary 53, and of the relative values of the input voltages to control grids of these tubes, it can be assured that at a particular average input voltage Vi the output voltage of fundamental frequency derived from the secondary of transformer 54 will be substantially zero. At other voltages than Vi, however, one or the other of tubes I and II will have a greater outputthan the other, so that a corre sponding output will be derived from transformer 54, producing a carrier-suppressed wave. 4

Generally speaking, the differing amplification characteristics of tubes I and II can be provided by selecting these tubes to be of different types. Alternatively, it can be provided by operating the tubes of the same type with different excitations, as is shown in Fig. 8.

Fig. 9 shows still another way of providing these different characteristicsin which differing biases are applied to control grids of. the tubes I and II, so that they will operate at different portions of their plate characteristics, having different curvatures. Other Ways of providingthese different curvatures may also be used. p

In most instances the difference in amplification characteristics of the two tubes will'necessitat'e operating at least one of them upon a as is well known, tends to produce distortion. Such distortion is evidenced by demodulation or by the production of harmonics of the carrier and side band frequencies. By supplying a suitable band pass filter 56, adapted to pass all frequencies in the neighborhood of the desired carrier frequencyto the output of transformer l,- a1l of stantially pure carrier-suppressed modulated wave.

Alternatively, the device may simultaneously frequency multiply, by passing only a harmonic of the input carrier. I

It will be noted that the device of Figs. 8 and 9 is completely independent of frequency, except for the band pass filter 56 which eirectively is merely a refinement of the circuit. Accordingly, the circuit can operate satisfactorily over a wide range of nominal carrier frequencies. It will be clear that further modifications can be provided similar to Figs. 8 and 9 all operating upon the principle described with respect to Figs. Sand 7.

While the systems of Figs. 6 to 9 have been described with respect to suppressing the carrier component of modulated waves, it will be seen that they can also be utilized to increase the percentage modulation of such modulated waves. Thus, if the minimum amplitude of the modulated wave input is adjusted to have the voltage value Vi, the output Wave derived from the apparatus of Figs. 6 to 9 will have its percentage modulation increased to substantially 100%. Similarly, if the" maximum value of the modulator wave to be ex-" pected is adjusted to have the value Vi, a similar increase in percentage modulation will result.

By other adjustments of the voltage of the modulated wave, the percentage modulation may be increased to other values;

If desired, an automatic modulation control circuit similar to thatof Fig. 4 may be provided. Fig. 10 shows one such circuit.- Here the modulated input Wave is supplied-to the modulation control circuit 58 of any of the Figs; 6 to 9 through an amplifier 57 having controllable amplification. The amplification of amplifier S'I maybe Scon trolled to maintain the average voltage "inputto the control circuit 58" at any desired value" For example,- the output derived from" control circuit whose output'is then connected in series 'withan adjustable bias" indicated schematically my; the? bias insertion circuit 6 l'.

I The combined' voltages, thus produced serves-to-control amplifieij'fil to maintain the input to control circuit*58"at the desired operating point:

The circuit of Fig. 10 is obtaining i carrier-suppressed outputs, "sin'oe"it' is g 60 particularly useful in for such an output-that the-average rectified 'cutg,

put voltage will be a minimum, whichfisa condf tio'nthat may readilybe' maintained "by the cirto control the modulatiorr'accordingly."

Fig: 11 shows a modified fdrih ofthe' it Fig. 10, includinga modifiedformofjthefmodula tioncontrol circuit of Fig.6.; 1h 'Fig'sll themedulate'd iinput wav is supplied to' a limiter circuit 62% of any V desired typeadapt-ed' in" well" known manner to produce an tially constant -amplitudeI output having a 'substan': I red P 55 of theout'put of limiter 62 the actual'carrier wave before mcdiiiaticnmay-be utili2ed p g The' modulatedwa've is also ffed t'o' a controllable ute ci iimitere2 ahd'ampiifier' si 'are combined in the combining circuit 5| to produce the'desire'cl' modified output.

. using rectifier 59, the

with the variable bias provided by circuit 61 to control amplifier 5'1. The limiter 62 provides a characteristic III shown 7, which, when combined with the characteristic II of the ampliher 57, provides a characteristic similar to I- -II of Fig. 7, and usefulin the same'manner.

By controlling the amplification characteristics of amplifier 57 in the manner shown in Fig-11, the circuit may be made to operate at any desired point of the characteristic II I, under the con-. trol of the bias provided-by circuit 6|.

Fig. 12. provides Fig. 11, but'adding a modified form of automatic modulation control. In thisinstance instead of output of the combiningcircuit 51 and of limiter 62 are supplied to-a balanced mixer 63. Balanced mixer 63 operates 4 to provide a reversible polarity direct current output-reprein a, manner similar to that of Fig.

senting a'deviation of the outputof the apparatus from the carrier-suppressed condition, that from the operating point vi. y adding to this output a variable-direct current bias provided by;

circuit Bl', the amplifier 51 may be controlled to maintain in operation the system at any desired this manner autopoint of the characteristic. In matic modulation control is; provided. H Accordingly I have provided an improved type of modulation control system which is responsive- I .to the amplitude of the'fin'p'ut modulatedwave, and 'is in no way responsive to oraffected-by variations in carrier frequency- This device, as

indicated above, ma be utiliied on. high .frequencies or low'frequencies.

As many changes could be made inthe abo v e construction and manyapparently widely dif ferent embodiments of 'this' invention could be. made without departing'from'the scope thereof, 1

it is intended'that all matter contained in the above description or shownin the accompanying drawin'gsshall be interpretedas illustrative and not in a limiting sense. What is claimed is:

lfApparatus for removing themodulation of a f modulated high frequency wave; comprising a velocity modulation electron discharge "device,

for producing astr'eam of electrcms,' means energized by said wave for velocity grouphaving means ing said electr' frequency energy from said put versus output characteristic; and means for causing'said extracted energy to have subs tam tially zero "percentage modulation; comprising meansfor adjustingtheaverage'amplitudeof said modulated energizing wave to 'val'ue corre spending to a maximum or'ininimum'ofthe input versus output characteristic of said devicet 2. Apparatus for suppressing the-carrier of a modulated high frequency wave comprisingfa velocity-modulation electron discharge device hav ing means for producing a stream of electrons,

means responsive toQsaid wave for varying the nor of saidextracted energy comprising 'means' for adjusting the'average amplitude of said modulated wave to input voltage characteristic of said device.

3. Apparatus for modifying "the a circuit similar to thatof on's, andmeans for egrtractin'ghigh v t ant d stream whereby sai'd'device has'an oscillating in-j a value substantially equal to that producing a zero of'the output voltage 'versus' percentage modulation of a modulated high'frequencywave comprising a velocity modulation electron di's charge i device having *meahs for producing a stream of electrons, means responsive to said waves for varying the velocity of said electrons,

and means for extracting high frequency energy from said velocity-varied stream; and means for causing said extracted energy to have a percentage modulation modified with respect to that of said modulated Wave, comprising means for adjusting the average amplitude of said modulated wave to a value corresponding to a point of the input voltage versus output voltage characteristic of said device having a negative slope.

4. Apparatus for controlling the modulation of a modulated high frequency wave, comprising means for producing an electron stream, means for velocity-grouping the electrons of said stream, means for extracting energy from said grouped stream, whereby the relation between the excitation of the grouping means and the energy derived from the extracting means displays an oscillating characteristic having an initial linear portion, and means for exciting said grouping means with said modulated wave at an average amplitude greater than that required to produce operation at said linear portion, whereby said extracted energy will have a percentage modulation different from that of said modulated wave.

5. Apparatus for controlling the modulation of a modulated high frequency wave, comprising a high frequency translating device having means for producing an electron stream, means for velocity-grouping the electrons of said stream, and means for abstracting energy from said grouped stream, whereby said device has an input versus output characteristic having an initial linear portion and subsequent non-linear portions, and means for exciting said grouping means with said modulated wave at an average amplitude greater than that required to produce operation at said portion, whereby said extracted energy will have a percentage modulation different from that of said modulated wave.

6. Apparatus for controlling the modulation of a modulated high frequency wave, comprising means for producing a stream of electrons, means energized from said wave for velocity grouping said electron stream, means for abstracting energy from said velocity-grouped stream, and means for causing said extracted energy to have a percentage modulation difierent from that of said modulated Wave, comprising means for adjusting the average amplitude of said modulated wave to a value greater than that required to produce a linear relation between the amplitudes of said input wave and said abstracted energy.

7. Apparatus as in claim 6, further including means for automatically controlling said amplitude-adjusting means in response to said extracted energy to maintain said diiferent percentage modulation.

8. Apparatus for controlling the modulation of a modulated high frequency wave, comprising a translating device having means for producing a stream of electrons, means for velocity-grouping said stream, and means for abstracting energy from said grouped streams, whereby said device has an oscillating input versus output characteristic having a linear first portion; means for energizing said grouping means from said modulated Wave, and means for causing said extracted energy to have a percentage modulation different from that of said modulated wave, comprising means for adjusting the amplitude of said energizing wave to a value greater than that required to produce operation of said device on said linear first portion.

9. Apparatus for controlling the percentage modulation of a high frequency modulated signal comprising a high frequency repeater of the velocity-grouped electron discharge type having an input versus output amplitude characteristic with an initial linear portion and subsequent non-linear portions, means for supplying said si nal to said repeater at an amplitude producing operation beyond said linear portion of said characteristic, whereby the percentage modulation of the output of said repeater is difierent from that of the input, and means for controlling said supplying means to control said percentage modulation.

10. Apparatus as in claim 9, further including means for actuating said controlling means in response to the output of said repeater to maintain said output signal at a predetermined percentage modulation.

11. Apparatus as in claim 9, wherein said con-. trolling means comprises means for comparing the output of said repeater with said signal to obtain a comparison signal, and means for actuating said supplying means by said comparison signal.

12. Apparatus for modifying the modulation of a modulated wave comprising a pair of electron discharge devices having equal outputs for a predetermined input amplitude and having differing input versus output characteristics, means for connecting the outputs of said devices in opposition, and means for supplying said wave to the inputs of said devices, whereby for input amplitudes of said wave in the neighborhood of said predetermined amplitude the opposed outputs of said devices have a modulation differing from that of said input.

13. Apparatus for controlling the modulation of a modulated high frequency wave, comprising translating means adapted to produce an output signal whose amplitude is an oscillating function of the amplitude of an input signal thereto, said oscillating function having a linear portion at relatively low input signal amplitudes, and means for exciting said translating means with said modulated wave at an average amplitude greater than that required to produce operation on said linear portion.

14. Apparatus for automatically controlling the modulation Of a modulated high frequency wave comprising repeater means for said wave adapted to modify the percentage modulation of an input wave for predetermined values of input ampli tude, said repeater means having an input circuit and an output circuit, and means connected to said input and output circuits for maintaining said input wave at an amplitude value yielding a desired output percentage modulation.

15. Ultra high frequency mixer apparatus comprising a pair of coupling loops having a common conductor, means for exciting said loops by one of said waves to be mixed, means for exciting said common conductor by a second wave to be mixed, and a respective rectifier connected to each of the remaining conductors of said loops, said rectifiers having a common terminal, whereby the unidirectional component of the potential of said common terminal will represent a mixed version of said two waves.

16. Ultra high frequency mixer apparatus for mixing two input waves, comprising a pair of coupling loops having a common conductor, means for exciting said loops in opposite phase by one of said waves, means for exciting said common conductor by the second of said Waves, and asymmetrical conducting means connected to each of the remaining conductors of said loops and having a common terminal, whereby the unidirectional component of the potential of said common terminal will represent a mixed version of said waves.

17 Ultra high frequency mixer means comprising a hollow cavity resonator adapted to be energized by a first wave, two coupling loops having a common central conductor, said coupling loops being inserted within said resonator to be excited by the field thereof, a transmission line adapted to be energized by a second wave and having the inner conductor thereof connected to said central conductor, and a rectifier connected to each of the remaining conductors of said loops and having a common terminal, whereby the unidirectional voltage between said common terminal and ground will represent a mixed Version of said two waves.

18. Apparatus for modifying the percentage modulation of a modulated high frequency wave comprising electron discharge means adapted to produce a zero output for a predetermined nonzero value of input, said means comprising a pair of channels having their outputs connected in opposition, one of said channels having a difi'erent input versus output characteristic from the other of said channels and said channels being adapted to provide equal outputs at said predetermined input value, means for supplying said modulated wave to the input of said electron discharge means, and means for adjusting the average amplitude of said modulated wave to a value in the neighborhood of said predetermined value,

19. Ultra high frequency apparatus comprising a cavity resonator, a pair of coupling loops having a common conductor and inserted within said resonator to be excited by the field thereof, a transmission line having the inner conductor thereof connected to said common conductor and the outer conductor connected to the exterior of said resonator, and a pair of series-connected detectors connected between the other conductors of said loops.

20. High frequency mixer apparatus for mixing a pair of input voltage waves comprising a pair of rectifiers connected in series arrangement and having a common terminal, a load resistor connected to said common terminal, means for connecting said two voltage waves in series across one of said rectifiers and said load resistor in series, means for obtaining a phase-reversed version of one of said input voltage waves, and means for connecting said phase-reversed version in series with the other of said voltage waves across the other of said rectifiers in series with said load resistor, whereby the unidirectional voltage across said load resistor will represent a mixed version of said two voltage waves.

21. High frequency apparatus comprising electron discharge translating apparatus having an input and an output, means for exciting said input by an input high frequency wave, means for mixing a version of said input wave and a wave derived from said output, and means coupled to the output of said mixing means for controlling the amplitude of said input wave.

RUSSELL H. VARIAN.

REFERENCES CITED The following references are of record in the file of this patent:

, UNITED STATES PATENTS Number Name Date 2,032,312 Ring Feb. 25, 1936 2,045,796 Plebanski June 30, 1936 2,193,578 Bruce Mar. 12, 1940 2,242,275 Varian May 20, 1941 2,304,377 Roberts Dec. 8, 1942 

